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Capacitive displacement gages provide precise measurements of distance and/or distance change. Such gages employ a capacitive displacement sensor (henceforth called the probe) whose sensing area is typically placed parallel to the target to be measured. In most applications, the area of the target is much larger than that of the probe. There are, however, applications in which the target size may be small enough to be close to the size of the capacitive sensor. Such measurements are often difficult to make by using traditional capacitance gaging systems since the output of the gage becomes sensitive to the alignment between the probe and target. It would be desirable to have a capacitive displacement sensor for measuring thin targets which is generally insensitive to the alignment between the probe and the target.
A capacitive displacement sensor for measuring thin targets is presented. The plate of the measurement probe of the sensor is designed to take into account the thin target shape and to provide accurate measurements of the thin target by reducing lateral movement sensitivity of the plate. The probe may also include a guard to reduce or eliminate capacitive coupling of the plate with other structures which would affect the accuracy of the measurement.